[clang] [clang-format] Introduce "ReflowComments: IndentOnly" to re-indent comments without breaking internal structure (think Doxygen). (PR #96804)

[Iuri Chaer via cfe-commits]

ichaer wrote:

@mydeveloperday, @HazardyKnusperkeks, do you have any more feedback?

I just noticed I didn't share this information before, but this is functionality Splunk is using internally to ensure `clang-format` fixes the indentation of our legacy doxygen comments without breaking their internal structure, and we'd like to contribute it upstream as we expect others must have similar problems.

https://github.com/llvm/llvm-project/pull/96804